These days, there are a number of different cooking oils available at the average grocery store—some of which are very familiar to us (e.g., olive oil) while others less so (e.g., palm oil).  For the purposes of this article, the term cooking oil refers to oil that has been mechanically extracted from the fruit or fruit seed of  a specific plant and processed into an edible form of oil. While the health benefit to harm ratio of most cooking oils is debatable (olive oil, for example^1,2), cooking oils are widely used in food preparation around the world, whether the food is home-cooked, prepared in a restaurant, or mass-produced and packaged in a factory. Thus, it is important to be knowledgeable of the different types of cooking oils you might encounter when making dietary choices. Here, we review the extraction methods, variations, reported health effects, and impacts on the environment of the most popular types of vegetable oils.

OLIVE OIL

Extraction methods and varieties. After being picked from the trees, the olives are mechanically pressed into a paste from which the oil is extracted.⁶ There are three main types of olive oil: extra virgin, virgin, and light. Extra virgin and virgin types are considered unrefined oils because once the oil is extracted from the paste, no other processing, added chemicals, or heat are used. Extra virgin olive oil (EVOO) is considered the highest quality of the three main types due to its lower acidity, darker color, and more intense taste and smell, compared to the other types. While made using the same process as EVOO and still considered high quality, virgin olive oil is slightly more acidic with a less distinguished color, taste, and smell than EVOO. Extra virgin and virgin olive oils have low smoke points, which means they cannot tolerate high cooking temperatures for very long. Light olive oil has been refined to increase its shelf life and smoke point. It is lighter in color with minimal, is any, taste or smell.

Health effects. EVOO contains antioxidant and polyphenolic components that have been linked better cardiovascular health, digestive tract functioning, and overall health.^1,4,7

Environmental effects. Olive oil production can be harmful to the environment, particularly in terms of soil erosion and habitat degradation, because of its high economic demand and its intensive cultivation.⁸

VEGETABLE OIL

Extraction methods and varieties. term vegetable oil is used to describe any type of edible oil that comes from plant sources, but typically, it refers to products that are a blend or combination of canola, corn, soybean, safflower, palm, and/or sunflower oils.⁴

The typical manufacturing process of vegetable oil begins with mechanical extraction followed by chemical extraction (hexane). Some small-scale or local manufacturers may not need to use chemical extraction or refining processes to produce their products, while others may use varying levels of refining (heat, filtering) to achieve desired characteristics (taste, color, smoke point). Large-scale manufacturers, on the other hand, typically use mechanical extraction, followed by filtering, heat, and chemical  processes, to produce their vegetable oil products.⁹

Health effects. The healthiness of the vegetable oil blend depends on the oils used in the blend, how they are processed, and how the blend is used. Given this, there is controversy and conflicting evidence regarding how nutritious vegetable oil blends are. The more processed/refined the oils are, the less nutrients they contains.^9,11 Vegetable oil blends also tend to be high in omega-6 fatty acids, which can increase inflammation.¹² However, the American Heart Association considers canola, corn, olive, peanut, and sunflower oils, including blends or combinations of these oils, as healthier alternatives to “tropical” cooking oils that contain more saturated fats (such as coconut or palm).¹²

Environmental effects.  Industrial-scale farming that focuses on single crops of the plants used to produce vegetable oil blends causes a number of environmental problems. Habitat loss, soil erosion, destruction of biodiversity, and pollution of soil and streams are just a few of the negative environmental effects of industrial farming.¹⁰

CANOLA OIL

Extraction methods and varieties. A relatively new addition to edible oil market, canola oil was developed in the 1970s by researchers at the University of Manitoba in Winnipeg, Manitoba , Canada—hence the prefix “can” for Canada.^3,12 Canola oil is extracted from the seeds of rapeseed, a flowering plant that is a member of the mustard family. Most manufacturers use both mechanical and chemical processes to extract the oil, with additional refining techniques, including bleaching and deodorizing.¹³ An unrefined (cold-pressed) version does exist, but can be costly and difficult to find.

Health effects. Canola oil is considered by many researchers to be one of the healthiest vegetable oils, due to its low saturated fat and high monounsaturated fat content.¹² Canola oil has been shown to reduce plasma cholesterol levels and have positive effects on other biological functions that impact overall disease risk.¹⁴ Unfortunately, canola oil tends to be highly processed, which means most, if not all, of its nutritional content has been stripped away. 

Environmental effects. Rapeseed is not considered a sustainable crop when grown large-scale, as is often required to fulfill the market demands for canola oil. It’s vulnerability to disease and pests requires the heavy use of nitrogen fertilizers, fungicides, and insecticides, which leach into nearby water and soil ecosystems.¹⁵

PEANUT OIL

Extraction methods and varieties. Peanut oil is extracted from the edible seeds of the peanut plant.¹⁶ Like olive oil, peanut oil comes in several varieties—refined, cold-pressed, gourmet, and blends. Refined peanut oil has been highly processed to remove the proteins responsible for peanut allergies. This oil is commonly used by fast-food restaurant chains in their fryers because of its high smoke point. Cold-pressed peanut oil is extracted from crushed peanuts. No heat or other refining processes are used in the extraction process, which allows the cold-pressed varieties to retain their nutrients and nutty flavor. Gourmet peanut oil is also unrefined, but it is made from roasted peanuts, which gives it a more intense nutty flavor. Sometimes, refined peanut oil is blended with other refined oils, such as soybean oil, to produce a more economical oil with a high smoke point.

Health effects. Because cold-pressed and gourmet peanut oils are unrefined, they retain their nutritive components. They are high in monosaturated fats, which have been shown to reduce cardiovascular disease risk, help with long-term weight maintenance, and improve insulin sensitivity.^16,18 They are also rich in vitamin E, an antioxidant that protects and strengthens cell longevity. However, peanut oil is high in omega-6 fatty acid, which is pro-inflammatory and prone to oxidation, which can cause free radicals and other harmful compounds to trigger premature aging and increase risk for certain cancers and heart disease.¹⁶

Environmental effects. Peanuts are considered a sustainable crop. Peanut crops can replenish soil with nitrogen depleted by other crops. Peanut crops require little fertilization, which reduces risk of water and soil contamination. Peanut crops also have deep root systems, which prevent soil erosion and decrease or, depending on the region, completely eliminates the need for irrigation.¹⁷

AVOCADO OIL

Extraction methods and varieties. The process for extracting oil from ripe avocados is similar to olive oil with the additional steps of removing the skin and seed. The flesh of the avocado is pressed and the oil is extracted. Avocado oil can be refined or unrefined.^20,21 Notably, this oil is versatile, being useful for skin care and for cooking.

Health effects. Unrefined avocado oil has a high concentration of antioxidants, including lutein, which may reduce the risk of cataracts, macular degeneration, and other common age-related eye diseases.²² Avocado oils are also rich in monounsaturated and polyunsaturated fatty acids, which have been shown to improve heart health by preventing inflammation and reducing bad cholesterol, as well as possibly improve wound healing.^2,11,22 However, this type of oil can be expensive and difficult to find.

Environmental effects. Industrial-scale avocado farms are not sustainable. Currently, 75 percent of the world’s avocados come from Mexico, which has resulted in avocado monoculture—the cultivation of a single crop in an agricultural region. Because avocados have become a major source of income for Mexico, avocado crops are given priority over other indigenous food crops, decreasing food security of the local communities. Avocado monoculture makes the avocado trees more susceptible to disease, while negatively impacting regional biodiversity through deforestation, soil nutrient depletion, habitat loss, and water and soil contamination by chemical fertilizers. Avocados are also water-intensive crops, and most of the water used for irrigation remain inside the avocados, which, once harvested, are shipped elsewhere; thus the local ecosystem is depleted of a natural source of water, negatively impacting access to drinking water in many local communities.²³

COCONUT OIL

Extraction methods and varieties. This tropical oil is extracted from pressed fresh or dried coconut meat. “Virgin” coconut oil is expressed from fresh coconut meat, while refined coconut oil is expressed from dried coconut meat. Unlike olive oil, using the terms “extra virgin” and “virgin” to distinguish coconut oil quality is not regulated.²⁵

Health effects. While coconut oil is versatile, it should either be avoided altogether or consumed in moderation, depending on who you ask.²⁴ A survey found that 72 percent of Americans rated coconut oil as “healthy,” though only 37 percent of nutrition experts agreed.²⁵ The main point of contention is its high saturated fat content. Coconut oil is 100-percent fat, 80 to 90 percent of which is saturated.²⁵ Evidence shows that coconut oil raises blood levels of artery-damaging LDL cholesterol.²⁶ Furthermore, this oil contains no cholesterol or fiber and only trace amounts of vitamins and minerals.

Environmental effects.  Around 70 percent of the world’s coconut supply is produced by small, family-owned farms in the Philippines, Indonesia, and India. Unfortunately, despite the high demand for coconuts, these farmers are paid very little for their crops, which makes it difficult for them to reinvest in their farms to help keep them viable (e.g., purchase equipment, protect the trees from pests, financially withstand damage caused by typhoons and other environmental factors). Additionally, the current global demand for coconuts is greater than what these small farms are able to produce. This is partly due to aging coconut trees, which produce fewer coconuts as they age. The farmers cannot afford to wait up to five years for young trees to start producing.²⁸

PALM OIL

Extraction methods and varieties. This tropical oil is extracted from either the fleshy fruit of the oil palm tree or its fruit’s seed kernels, and is one of the most widely produced edible fats in the world.^29,30 The oil derived from the fleshy fruit is called crude palm oil, which comprises the most popular edible forms, whereas the oil derived from the fruit’s seed kernels is called palm kernel oil, which is primarily used in commercial cooking, cosmetics, and pharmaceuticals. Like coconut oil, it is versatile and semi-solid at room temperature due to its high fat content.

Health effects. Palm oil is 100-percent fat—in palm kernel oil, 80 percent of this fat is saturated compared to 50 percent in crude palm oil. Like other vegetable oils, the more processed and refined the oil is, the less nutritive value it retains. Crude palm oil with minimal refinement has a reddish color because it contains a fair amount of carotenoids, which have beneficial antioxidant effects. It contains vitamin E, specifically tocotrienols, an antioxidant that supports brain health by protecting the delicate polyunsaturated fats in the brain, slowing dementia progression, and reducing the risk of stroke.³⁰ Palm oil’s effect on heart health is mixed, with effects of lowering certain risk factors for heart disease only being reported for certain groups of people. Furthermore, repeatedly reheating this oil may decrease its antioxidant properties and add to cardiovascular disease risk.^11,30

Environmental effects. Palm oil is notorious for its detrimental impact on the environment in Southeast Asia, where it is grown. Replacing tropical forests and peatland with palm oil trees has devastated the natural ecosystems, wildlife habitats, and quality of life of the native people.³⁰

SUNFLOWER OIL

Extraction methods and varieties. Sunflower oil is extracted from the pressed seeds of the Helianthus annuus plant. There are four types of this oil available in the United States—high linoleic, mid-oleic, high oleic, and high stearic/high oleic­—all of which are produced for different nutrient compositions based upon their levels of linoleic and oleic acid.^31,32

Health effects. All sunflower oils are 100-percent fat and contain vitamin E.³¹ Some research suggests that consuming high oleic sunflower oil in place of saturated fats may reduce risk of heart disease by lowering LDL (bad) cholesterol and raising HDL (good) cholesterol.³³ In fact, the US Food and Drug Administration supports the health claim that oils containing at least 70-percent oleic acid may reduce coronary heart disease. However, sunflower oils can release toxic compounds when heated to high temperatures.³⁴ Some varieties are also high in omega-6, which contributes to inflammation in the body when consumed in excess.³¹

Environmental effects. Sunflowers are considered a sustainable crop in the US, where they are a native plant species. Sunflowers can be planted as cover crops to improve and protect soil in between planting of other crops. Sunflowers require very little fertilizer, no irrigation, and limited use of pesticides. Additionally, they are beneficial to the ecosystem by attracting pollinators, removing contaminants from the soil, balancing bacteria in soil, and providing food for wildlife over the winter.³⁵

SESAME OIL

Extraction methods and varieties.  This versatile seed oil is extracted from raw or toasted pressed sesame seeds. Oil made from raw, pressed sesame seeds is considered a neutral oil and is similar to canola oil. It can be used for frying and roasting foods. Oil made from toasted sesame seeds is a different story. It is more expensive than its raw form, has a very intense, distinct taste, and burns very easily when heated. Toasted sesame oil is generally used as flavoring only, not cooking. Just a few drops impart an intense, nutty flavor to foods.

Health effects. While sesame seeds are high in protein and B-vitamins, refined sesame oil doesn’t contain the protein or many of the essential vitamins and minerals the seeds contain. However, raw, pressed sesame oil does retain important fatty acids.³⁶ This oil is known for its anti-inflammatory and antioxidant properties, which can potentially lower risk of cardiovascular disease and atherosclerosis, which is the buildup of fat and other substances in artery walls that causes these vessels to narrow and raises blood pressure.³⁷ While sesame oil is rich in omega-3 and omega-6 fatty acids, too much of any oil can lead to unwanted effects, such as weight gain.³⁶ 

Environmental effects. While sesame seeds are naturally drought resistant, much of the US-grown sesame is intercropped with cotton, a crop that is nearly entirely genetically modified (GM) and requires a large amount of herbicides, which can build up in the ecosystem over time, negatively affecting plant and animal life.³⁹

WHICH OIL IS BEST?

Each type of vegetable oil has its own unique characteristics, health effects, and environmental impacts. So, when choosing an oil, consider the types of fat it contains and its nutrition profile in relation to your personal health goals and needs. Its stability (smoke point), degree of refinement, whether/how nutrition content changes during cooking, and how heat will affect its flavor are also important considerations. And finally, the impact that cultivating and processing a particular oil has on the environment might be worth investigating before making your purchase…to avoid inadvertently supporting a harmful industry.

Editor’s note. Adhering to nationally recognized dietary guidelines regarding the consumption of fats and oils is important to your overall health. Moderation is key, and completely avoiding fat in the form of processed oils, even those that are unrefined, might be the healthiest option for many people. Consult with a licensed healthcare professional to determine how consumption of oils might impact your health, especially if you have pre-existing health conditions, such as diabetes or heart disease, are pregnant or lactating, or wish to reduce or increase your weight.

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